1. Field of the Invention
The present invention relates to a method and system for expanding tobacco made by shredding tobacco leaves with an expanding agent such as carbon dioxide, and heating, expanding, and drying the tobacco impregnated with the expanding agent.
More particularly, the present invention relates to a method and system for preventing the aroma of tobacco and the smoking taste from deteriorating in the following processes. The tobacco impregnated with the expanding agent is continuously fed into the flow of high-temperature gas containing stream, dispersed in the gas-flow, flown together with the gas, and heated while the tobacco flows together with the gas, and the expanding agent impregnated in the tobacco expands to expand the texture of the tobacco and the tobacco is dried while heated. Steam or water is externally injected to a channel where the gas and tobacco flow and the gas temperature is controlled to expand and dry the tobacco.
2. Description of the Related Art
Conventionally, tobacco is expanded to moderate the smoking taste and decrease the cost by decreasing the amount of tobacco used.
The material is expanded by impregnating the tobacco texture with an expanding agent such as freon or carbon dioxide before heating the tobacco to quickly expand the expanding agent impregnated in the tobacco and the tobacco texture.
Recently, however, carbon dioxide is used for the expanding agent in order to avoid affecting the environment. When the expanding agent uses carbon dioxide, it easily goes out of the tobacco. Therefore, it is necessary to quickly heat the tobacco impregnated with carbon dioxide and quickly swell the impregnated carbon dioxide and the tobacco texture.
To heat the tobacco impregnated with the expanding agent, a method is conventionally used to dry tobacco by applying hot air to it while it is carried by a net conveyor. Another method is also conventionally used at times for drying tobacco by applying hot air and infrared rays to it while it is carried by a net conveyor.
For the above methods, however, it is difficult to quickly heat tobacco and, in addition, the impregnated carbon dioxide is almost lost before the tobacco material is expanded because of a low heating speed when the expanding agent uses carbon dioxide.
There is still another tobacco drying method for feeding tobacco into the flow of high-temperature gas. For this method, the tobacco fed into the high-temperature gas is dispersed and flows together with the gas. Therefore, it is possible to quickly heat the tobacco with the high-temperature gas. The high-temperature gas uses, for example, a gas made by mixing air with 50 to 95 volume percent of superheated water vapor. Because the mixture gas consisting of air and superheated water vapor has a large specific heat, the tobacco fed into the gas-flow can more quickly be heated.
Therefore, when the expanding agent uses carbon dioxide, the method of feeding tobacco into the above high-temperature gas-flow is suitable for heating the tobacco impregnated with carbon dioxide.
For the method of feeding tobacco into the high-temperature gas-flow, however, there is the disadvantage that the tobacco fed into the high-temperature gas-flow is burnt and the aroma of the tobacco and the smoking taste are degraded because a large heat quantity is given to the tobacco from the high-temperature gas though the tobacco can quickly be heated.
When the expanding agent uses, for example, carbon dioxide, it is necessary to feed the tobacco into the gas-flow containing more than 50 volume percent of water vapor and having the temperature of 200.degree. to 350.degree. C. in order to adequately swell the tobacco impregnated with carbon dioxide. However, the texture of tobacco leaves is burnt when the temperature of tobacco exceeds 140.degree. C., and the aroma and the smoking taste are degraded when the temperature of it exceeds 180.degree. C. because the sugar contained in the tobacco leaves decomposes.
Therefore, when the agent uses carbon dioxide and the tobacco impregnated with the carbon dioxide is fed into high-temperature gas-flow to expand and dry tobacco, it is necessary to quickly contact the tobacco with the high-temperature gas so that the tobacco is adequately expanded and to prevent the aroma and the smoking taste from degrading. However, it is difficult to control contacting of the tobacco fed into the high-temperature gas-flow with the high-temperature gas and heating of the tobacco so that it meets the above conditions. To control heating of the tobacco fed into the high-temperature gas-flow, various methods and systems have been developed so far.
For example, the official gazette of Japanese Patent Laid-open No. S59-6875 discloses a method and system for feeding tobacco into high-temperature steam flow and installing a tangential separator at the down-stream side of the tobacco feed port. In this case, the tobacco fed from the feed port contacts high-temperature gas and flows together with the high-temperature gas, and it is separated from the high-temperature gas by the tangential separator. Therefore, it is possible to securely control the contacting time between the tobacco and the high-temperature gas and the heating state of the tobacco by controlling the distance between the tobacco feed port and the tangential separator and the gas-flow rate. The official gazette also discloses a method for feeding tobacco into the tangential separator to contact the tobacco with high-temperature gas only for a very short time before it is immediately separated from the gas.
The official gazette of Japanese Patent Publication No. S57-25194 discloses a technique for feeding tobacco into a pipe where high-temperature gas-flows and controlling the contacting time between the tobacco and the high-temperature gas at the range of 0.2 to 2.0 sec.
The technique for controlling the contacting time between tobacco and high-temperature gas is disclosed in these official gazettes. However, to adequately expand the tobacco and prevent the quality from degrading, reciprocal conditions must be met. Therefore, no adequate effect can be obtained only by controlling the contacting time between the tobacco and high-temperature gas as disclosed in these official gazettes.
How the aroma of the greatly-heated tobacco and its smoking taste are degraded is complex and delicate. For example, the tobacco fed into the superheated water vapor flow of 300.degree. C. maintains the practically-satisfactory quality when the contacting time between the tobacco and high-temperature water vapor is 1.5 sec. However, it does not maintain the practically-satisfactory quality for the contacting time of 1.6 sec. These characteristics are confirmed through the test executed by installing a separator at the down-stream side of a pipe where high-temperature gas-flows and changing side position where the tobacco is fed into the pipe and the time until the tobacco is separated from the high-temperature gas-flow after it is fed into the gas-flow.
Moreover, the expanded tobacco containing much water would shrink after it expands. Therefore, to prevent the expanded tobacco from shrinking, it is also clarified that the expanded tobacco should be brought under almost absolute dry condition with the water content of 2 to 3 weight percent.
In short, when the expanded agent uses carbon dioxide, it is necessary to feed the tobacco impregnated with carbon dioxide into high-temperature gas-flow and quickly heat it. In this case, however, it is necessary to control the contacting state between the tobacco and the gas, adequately expand the tobacco, and prevent its quality from degrading.